1. Technical Field
The present disclosure relates to a low-frequency sound reproduction system for high power output, and more particularly to a low-frequency sound reproduction system having a manifold, a low frequency speaker, and one or more passive radiators and/or air ports.
2. Discussion of the Related Art
A woofer is a loudspeaker driver that is designed to produce low-frequency sounds, typically from around 40 Hertz up to about a few thousand hertz. Nearly all woofers are driven by a voice coil in a magnetic field, connected to an amplifier. The voice coil assembly is an electric motor. When current flows through the voice coil wire, the coil moves according to Fleming's left hand rule, causing the coil to push or pull like a piston. The voice coil is typically cemented to the back of the speaker cone, which creates sound waves as it is pushed back and forth.
A sub-woofer is similar to a woofer, but is dedicated to the reproduction of bass frequencies, typically from about 20 Hz to about 200 Hz. Since it is difficult for small loudspeakers to reproduce frequencies below 80 Hz, especially above 100 dB, a loudspeaker intended specifically for this task is often used. There is a growing demand for compact, high-output subwoofer systems for use in both home and professional settings.
Many existing designs use horn loading to provide high efficiency and low distortion, but these systems are typically very large. Shorter horn-loaded systems such as those described in U.S. Pat. No. 5,898,138 detail a method of including multiple drivers, ports or passive radiators into a single horn throat. However, the very short nature of the horn severely restricts the efficiency gain and air load effectiveness at low frequencies. To obtain better efficiency and still keep a small enclosure size, some designs use a low frequency horn that is folded. U.S. Pat. No. 4,215,761 relates to a bass sound projection system which uses a folded horn. While this approach reduces the overall size of the system, it is still very large compared to a conventional sealed or ported enclosure.
An alternate solution to standard horn loading is called “manifolding” and was proposed in U.S. Pat. No. 4,733,749. This design increases efficiency and reduces distortion while allowing the use of relatively large loudspeakers in a very compact cabinet. This configuration optionally uses a sealed or ported cabinet, and the manifold may form the throat of a horn for even higher performance at the cost of increased size.
Other designs employ multiple chambers in various styles of bandpass enclosures. These systems can vary in size significantly, but the smaller designs are usually designed to have high mid-bass efficiency (50-150 Hz) and sacrifice low frequency extension. Most commercial applications also have a severely degraded transient response as a natural result of high-order upper and lower frequency rolloffs.
Alternate designs use passive radiators (drones) in place of ports as a method to decrease system size and reduce air noise inevitable from a standard port. A passive radiator ideally should be capable of very high excursion and of substantially greater surface area than the active woofer. A known commercial design with such features uses large woofers and multiple large passive radiators, both of which significantly increase the size of the speaker system. Another design uses very compact enclosures with multiple passive radiators, but these are very low in efficiency and require very powerful amplifiers to produce meaningful sound pressure level (SPL).
There exists a need to provide a new loudspeaker system to provide high output, low distortion, low noise, and extended frequency response.